Phenformin is a biguanide compound that has been used to treat diabetes, in particular, type 2 diabetes.

Despite its efficacy as a hypoglycemic agent, phenformin is no longer available for the treatment of diabetes in the United States due to its association with an increased risk of lactic acidosis. Metformin, another biguanide, has replaced phenformin in the United States for the treatment of diabetes.
The incidence of lactic acidosis associated with metformin is significantly less than that observed with phenformin.
Recent studies have indicated that phenformin may have antitumor activity. See Filippo Caraci, et al., “Effects of phenformin on the proliferation of human tumor cell lines,” Life Sciences, 2003 Dec. 19:74 (5):643-50; Dilman and Anisimov, “Potentiation of antitumor effect of cyclphosphamide and hydrazine sulfate by treatment with the antibiabetic agent, 1-phenylethylbiguanide (phenformin),” Cancer Lett. 1979 October; 7 (6):357-61. The mechanisms of how phenformin affects tumor growth must be elucidated in order to maximize the potential for success in using phenformin to treat cancer. Thus, there remains a need to identify whether phenformin will likely be effective in suppressing growth of particular tumor-types.
It is well known in the art that oxygen is a potent radiosensitizer that can increase the effectiveness of a dose of radiation by, for example, forming free radicals that can damage DNA. One of the limitations of radiation therapy used to treat cancer is that the cells of solid tumors become deficient in oxygen after exposure to radiation, resulting in a hypoxic environment. Tumor cells in a hypoxic environment can be 2 to 3 times more resistant to radiation damage than those in a normal oxygen environment. Harrison L. B., et al. Impact of tumor hypoxia and anemia on radiation therapy outcomes, Oncologist 7 (6):492-508. Thus, there remains a need to identify compounds that can sensitize cancer cells to radiation therapy.